BSC fails to deactivate formerly-active but now inactive SI in BTS
If we previously had a given SI present/active, we must send a zero-length BCCH FILLING for that SI type to the BTS to stop it from further transmitting this SI.
This was so far not caught with IP based BTSs, as we always dropped the OML link which meant a full re-initialization of the BTS state. However, with E1 based BTSs and with the new "bts <0-255> resend-system-information" VTY command, we can actually easily end up here. Simply enable a given SI type, resend SI, disable it, resend SI: The new set of active SI will be sent, while the now inactive SI will not be sent (but still remain active at the BTS).